1. Field of the Invention
The present invention relates to a sealed switch and a method for reducing an internal pressure in the sealed switch.
2. Description of the Related Art
There is known a neutral start switch (inhibitor switch) mounted on a vehicle to be used for detection of a selection range of a shift lever, as an example of this kind of sealed switch.
FIG. 10 shows a typical configuration of the neutral start switch. The neutral start switch 1 is configured such that a switch case 3 is formed of a plastic substrate 10 (polar substrate) and a lid body 35. Fixed contact points 20 of the neutral start switch 1 are mounted on the substrate 10 by insert molding, and movable contact points 54 which are connected to/disconnected from the fixed contact points 20 are arranged in a movable board 50 movably arranged in the switch case 3. The movable board 50 is rotatably supported through a shaft portion 55 to seal bearings 67 inserted into shaft holes 45 and 15 provided in the opposing portion between the lid body 35 and the substrate 10. The substrate 10 is formed in a fan shape on the basis of the shaft holes 45 and 15.
The fixed contact points 20 are specifically mounted to a plurality of rows of arc-shaped fixed-contact point mount portions 68 around the shaft holes 45 and 15 by insert molding. The movable contact point 54 is connected to/disconnected from the fixed contact point 20 with rotation of the movable board around the shaft holes 45 and 15, and the connection/disconnection allows the fixed contact point 20 and the movable contact point 54 to be electrically connected/disconnected, which thus performs the switching operation.
The fixed contact point 20 and the movable contact point 54 are coated with contact point grease for improving durability thereof and current-carrying properties at the contacting thereof. The fixed contact point 20 is provided with a connecting piece portion 21 integral therewith, and the connecting piece portion 21 is formed to be integral with the substrate 10 by insert molding as described above. The connecting piece portion 21 extends toward a connector portion 5 inside the substrate 10 and is exposed to an outside as a terminal of the connector portion 5 projecting from an outer surface of a side wall 12 of the substrate 10 to an outside.
The neutral start switch 1 is provided with seal bearings 67 between the shaft portion 55 of the movable board 50 and the shaft holes 45 and 15 for preventing water, mud or the like from entering into the switch case 3. In addition, the substrate 10 and the lid body 35 are air-tightly jointed with each other across the entire circumference of the substrate 10 and the lid body 35 by welding, and a seal ring (described later) is provided between joint surfaces of the substrate 10 and the lid body 35.
In a case of jointing the substrate 10 and the lid body 35 in the neutral start switch 1 by welding, a high joint strength is necessary. Therefore conventionally a share joint method excellent in the welding performance and a welding structure suitable for the share joint method are adopted.
FIGS. 11A and 11B and FIGS. 12A and 12B respectively show a welding structure (joint structure) between the substrate 10 and the lid body 35 in the neutral start switch 1 applied to the share joint method.
As shown in FIG. 11A, the substrate 10 is provided with a side wall 12 surrounding an entire circumference of the movable board 50 in a rotation region thereof and formed integrally with the substrate 10, and a ring groove 30 for accommodating the seal ring 31 and a concave streak portion 26 are formed on a top end surface 25 of the side wall 12 across the entire circumference of the side wall 12 in that order from the inside. A welding inclination surface 27 is formed in the depth of the concave streak portion 26 of the side wall 12 at an outer peripheral side. In addition, the lid body 35 is provided with a projecting streak portion 40 on a lower surface 38a of a flange portion 38 in the lid body 35 opposing the top end surface 25 of the side wall 12. The projecting portion 40 is fitted in the concave streak portion 26 of the side wall 12.
The projecting streak portion 40 extends across the entire circumference along a peripheral edge of the flange portion 38. A welding shoulder portion 41 for welding with the welding inclination surface 27 is formed in an intermediate portion of the projecting streak portion 40 at the outer peripheral side thereof. The welding inclination surface 27 and the welding shoulder portion 41 are configured such that when the top end surface 25 of the side wall 12 makes contact with the lower surface 38a of the lid body 35, the welding shoulder portion 41 of the projecting streak portion 40 is designed to interfere with the welding inclination surface 27 of the concave streak portion 26. As a result, when high-frequency welding causes the melting of the interference portion across the entire circumference, the projecting streak portion 40 and the side wall 12 are welded to be integral.
At the welding between the substrate 10 and the lid body 35, when the projecting portion streak 40 of the lid body 35 is in the process of being inserted into the concave streak portion 26 of the substrate 10 while interposing the movable board 50 between the substrate 10 and the lid body 35, as shown in FIG. 11B a corner of the welding shoulder portion 41 of the projecting streak portion 40 first makes contact with the welding inclination surface 27 of the concave streak portion 26. In this state a gap S1 remains between the top end surface 25 of the side wall 12 and the lower surface 38a of the lid body 35. The ring groove 30 has a depth smaller than a diameter of the seal ring 31 in a free state (no load state), and the seal ring 31 partly projects from the ring groove 30.
As the lid body 35 is further pressed to the substrate 10 from a position of FIG. 11B in the high-frequency applied state, the interference (overlap) portion between the welding shoulder portion 41 and the welding inclination surface 27 is melted, and the lid body 35 moves in the approaching direction relatively to the substrate 10. In addition, as shown in FIG. 12A after the lower surface 38a of the lid body 35 makes contact with the seal ring 31 in the ring groove 30, it presses the seal ring 31, and finally, as shown in FIG. 12B, the lower surface 38a of the lid body 35 is seated on the top end surface 25. Then the projecting streak portion 40 and the side wall 12 are jointed across the entire circumference by welding, and along with it, the inside of the switch case 3 becomes in a sealing condition by flexible deformation of the seal ring 31 between the side wall 12 and the lower surface 38a of the lid body 35.
In such a welding structure, however, the neutral start switch 1 is sealed by the sealing operation across the entire circumference of the seal ring 31, but there are some cases where the connector portion 5 gets wet with grease. In this situation, there is a possibility that durability of the fixed contact point 20 and the movable contact point 54 is degraded, and in some cases the leak of the grease itself takes for the event that water exists inside the neutral start switch 1. Further, there is a problem that the outside appearance and visual quality of the neutral start switch 1 get worse since dusts adhere to the leaked grease.
The inventors have found out the following matter as a result of repeatedly diligently studying factors of this leakage of the grease.                (1) The leak of the grease cannot be confirmed near the seal ring 31.        (2) As the pressure in the switch case 3 is measured, it is raised to pressures equal to or more than an atmospheric pressure.        From the results of the above (1) and (2), it is estimated that the grease applied to the contact point, for example, the fixed contact point 20 flows on the interface between the fixed contact point 20 and the plastic, and leaks into the connector portion 5. In addition, although the conductive-metallic fixed contact point 20 is insert-molded to the plastic substrate 10, it is estimated that a perfectly adhesive state is not formed between the fixed contact point 20 and the plastic.        
That is, in the joint structure of the substrate 10 and the lid body 35, since an inner space of the switch case 3 interposed between the substrate 10 and the lid body 35 starts to be blocked out from the outside from the position shown in FIG. 11B, the inner space is compressed by the gap S1 caused by the pushing movement of the lid body 35 during a period from the position in FIG. 11B to the joint completion shown in FIG. 12B. As a result, the welding shoulder portion 41 and the welding inclination surface 27 are welded with each other to increase the welding amount. During this period, the sealing operations between the shaft portion of the movable board 50 and the shaft holes 45 and 15 are also performed by the seal bearings 67, and the air inside the switch case 3 is not released to an atmosphere because of each structure of the switch case 3 and the seal bearing 67. Accordingly, it is estimated that the grease applied to the fixed contact point 20 in the substrate 10 is pushed out to the side of the connector portion 5 by the pressure in the switch case 3 after the welding between the substrate 10 and the lid body 35.
Accordingly, as described above, in the switch configured to form the sealed structure by interposing the seal ring 31 between the joint surfaces of the lid body 35 and the substrate 10, a hole for releasing the pressure in the switch case 3 is necessary.
It should be noted that Japanese Patent No. 3956433 discloses a technology that a breathing hole in response to a change in internal pressure of the switch case is provided in the switch case and a multi-hole semi-transparent film (Gore-Tex (registered trade mark)) is mounted to the breathing hole, thus suppressing a rise in the internal pressure of the switch case 3.
However, there occur problems that since the multi-hole semi transparent film is high in costs, it is difficult to adopt, since not only the multi-hole transparent film but also a film is exposed to an outside, it is susceptible to damages and the breathing is possibly difficult because of contamination of grease or the like, and at the time of picking switches and inspecting all of them, the measurement of internal pressures thereof is difficult because of difficulty in pressure measurement in the switch case through the breathing hole. In addition, for providing a hole of releasing a pressure in a plastic product, a change in a manufacturing line or an inspection line in regard to a mold, a line, an inspection or the like for the product is necessary, thereby creating a problem of increasing costs.
Therefore in the sealed switch, it is required to release a pressure inside the switch case without changing or modifying the structure thereof as much as possible.